Yes, it is very normal!
4.6 mmol/l is equal to about 83 mg/dl, which is the low end of normal. For people with diabetes, it usually takes a while to bring blood sugar back down after a meal but if you do not have diabetes, then it is perfectly normal for your body to naturally bring your blood sugar back down to the "fasting" range after an hour or so. Your body is just doing it's job and USING the sugar from your food, rather than letting it spill into your blood.
Unless you are feeling ill (shaky, dizzy, sweating, etc.) I would not worry!